The present disclosure relates generally to an internal combustion wave rotor combustion engine, and to a hybrid system including the wave rotor engine.
Wave rotor combustion engines have been developed as an improvement to the conventional combustor that requires a separate high-pressure compressor and high-pressure turbine. In one example depicted in FIG. 1, a wave rotor is integrated into a propulsion system such as a gas turbine engine 10. The engine includes a fan 12 supplying air to a low pressure compressor 14. The compressor feeds compressed air into a chamber 16 where the air is mixed with fuel injected through nozzle 18. The combustible mixture is provided to a wave rotor assembly 20 that combusts the air-fuel mixture in a succession of substantially constant-volume combustion events. The resultant combusted gas is provided to the inlet of a low-pressure turbine 22 which extracts power to drive the fan 12, compressor 14 and other accessories. The combusted mixture exits the turbine into a convergent nozzle 24 to form a high-velocity jet of hot gas.
One example of such a wave rotor assembly suitable for use in the engine 10 of FIG. 1 is disclosed in U.S. Pat. No. 6,460,342. The construction of one form of wave rotor assembly is generally depicted in FIGS. 2-4, with further details provided in the '342 Patent, the disclosure of which is incorporated herein by reference. As shown in FIG. 2, the wave rotor assembly 20 includes a rotor 50 with a rotor shaft 52 mounted for rotation within a housing 54. The housing defines an inlet port 55 for receiving compressed air and/or an air-fuel mixture through an inlet duct 56 (coupled to the compressor 14), and an outlet port 58 supplying combusted gas to an outlet duct 59 (coupled to the turbine 22). The rotor 50 includes a plurality of chambers 60 formed by vanes 62 extending radially from the hub 64 of the rotor and axially along the rotor from the inlet to the outlet. Fuel is injected into the inlet air stream by a feed line 70. An igniter 72 ignites the air-fuel mixture within the rotor 50. A motor 75 may be connected to the rotor shaft 52 to rotate the rotor 50. A controller 77 controls the motor, fuel injectors and igniter to control the timing of the detonative process within each of the chambers 60.
In operation, a deflagration flame or detonation wave 82 produced by ignition of the air-fuel mixture within a particular chamber results in substantially constant volume combustion. The hot gas generated by combustion exits into the outlet port 58, resulting in an expansion wave 83 which travels from the outlet end to the inlet end of a combustion chamber just as it rotates into communication with the inlet port 55. The resulting reduction of pressure draws new air into the chamber. The rotor continues to rotate through various inlet zones to receive a new charge of combustible air-fuel mixture and an oxidant until the chamber is in line with the igniter 72, whereupon ignition of the air-fuel mixture starts the cycle over again. The foregoing is a general description of the operation of the wave rotor assembly 20, it being understood that more details of the operation can be obtained from the '342 Patent incorporated herein by reference.
Aircraft electrification could cut operating fuel cost and environmental impact if a very efficient and powerful combustion engine can be provided that complements an energy-dense battery storage and a lightweight motor. Piston or rotary engines may be too heavy, and gas turbine engines too thirsty, but their best attributes unite in the wave rotor combustion (WRC) turbine engine described above. Beyond constant-volume combustion (CVC) thermodynamics, the WRC turbine merges compressor, combustor, and turbine functions into a single rotating component. Recent progress in fast deflagration, wave rotors, and high-density batteries enables the “hybrid wave-rotor electric aero-propulsion” (HyWREAP) technology to achieve quantum performance gains.
Conventional Brayton-cycle continuous-flow combustors allow free expansion which wastes energy. Ubiquitous in Nature, oscillatory and pulsatile flows are rarely exploited by human engineers. CVC offers high specific impulse and power over a wide Mach range with limited or no mechanical compression. For 737-class aircraft in the NASA-designated ‘N+3’ time frame, CVC was top-ranked by Boeing's Subsonic Ultra Green Aircraft Research (SUGAR) study for both fuel burn and landing/take-off (LTO) NOx. The SUGAR study also predicted up to 65% fuel cuts for hybrid-electric-gas turbine drive.
On the electrical side of the equation, the rapid pace of innovations for battery energy density and electric machines creates the potential for these technologies and the CVS technology to be highly synergistic. The present disclosure goes beyond ideas that consider pure electric propulsion or hybrid electric propulsion where a conventional gas turbine powers distributed propulsor fans. HyWREAP as described herein is an integrated and optimal approach to combining on-board energy sources of battery power and hydrocarbon fuel. For most transport aircraft with the relatively predictable duty cycle, the on-board batteries would not need to be recharged in flight even in the hybrid case that includes a combustion engine producing power. Rather, their state of charge would be carefully managed such that the airplane will use up all the battery power during intended parts of the duty cycle, whether taxiing, takeoff assist, portions of cruise, or landing. For some flight applications with less predictable or highly varying duty cycle, such as unmanned aircraft, the on-board batteries would be charged from the combustion engine power source, so as to maintain readiness for periods of high power or silent operation or power needs other than propulsion, such as data transmission or sensors.